Question

Possible Duplicate:
How should I store GUID in MySQL tables?

VARCHAR will return as string
BLOB will return as byte[]
but, what column type of MySQL will return as System.Guid in C#
thanks.

Edited: I have found the answer

thanks to DaveHogan that gives me the clue about ORM (Object Relation Mapping)
I started to look for information about the datatype conversion(mapping) made by Connector/NET.
I’m using MySQL Dot Net Connector (Connector/NET)
there are different 3 situations that Connector/NET performs.

Below are what I have found:

1st Situation:
Start from Connnector/NET 6.1.1, CHAR(36) will be automatically converted as System.GUID in C# and BINARY(16) will be treated as System.Byte[].

2nd Situation:
If you use older Connector/NET, BINARY(16) will be automatically converted as System.GUID when the value is passed into C# and CHAR(36) will be treated as System.String.

3rd Situation:
If you use newer Connector/NET (newer than 6.1.1), and if you want to use BINARY(16) AS System.GUID (be default it is not), you have to add a connection option Old Guids=true in the Connection String.
Example:

server=localhost;user=root;password=qwerty;database=test;old guids=true;

by this, CHAR(36) will be converted as System.String and BINARY(16) = System.GUID

Read more about connection options of Old Guids at:
MySQL 5.6 Reference Manual: 21.2.6. Connector/Net Connection String Options Reference

———————————————————————-
Extra Info:
How to Insert System.GUID into MySql Database
———————————————————————-
This is a sample table, that we are going to insert the System.GUID:

CREATE TABLE `testdata` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `binary` binary(16) DEFAULT NULL,
  `char` char(36) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8

Insert System.GUID into MySQL

string constr = "server=localhost;user=root;pwd=qwerty;database=test;";
using (MySqlConnection conn = new MySqlConnection(constr))
{
    conn.Open();

    // Create a System.GUID
    byte[] ba = new byte[16];
    Random rd = new Random();
    rd.NextBytes(ba);
    System.Guid guid = new Guid(ba);

    // Prepare GUID values in SQL format
    string guidForChar36 = guid.ToString();
    string hexstring = BitConverter.ToString(guid.ToByteArray());
    string guidForBinary16 = "0x" + hexstring.Replace("-", string.Empty);

    string sql = "insert into testdata(`binary`,`char`)"
               + "values(" + guidForBinary16 + ","
               + "'" + guidForChar36 + "');";

    MySqlCommand cmd = new MySqlCommand(sql, conn);
    cmd.ExecuteNonQuery();

    conn.Close();
}

Answer 1

EDIT:

Sorry I misunderstood your question. You should use

BINARY(16)

How you cast that to a System.Guid depends on whether you’re using an ORM etc.